Why did Ratcliffe defence fail where Kingsnorth Six succeeded?

Two separate trials of environmental activists that both targeted coal-fired power stations produced different results. Lawyer Mike Schwarz examines the reasons why

The Ratcliffe-on-Soar power station, Nottinghamshire. This week campaigners who planned to shut down the coal-fired power station were convicted of conspiracy to commit aggravated trespass. Photograph: David Sillitoe/Guardian

CO2 released by coal-fired power stations is the single most damaging contributor to climate change. So it is perhaps little wonder that concerned citizens have sought to close them down. However, the juries delivering their verdicts on their actions have come to conflicting conclusions.

Why the disparity? Although both sets of defendants sought to stop CO2 emissions from the coal-fired power stations, the charges they faced and the legal defences were different.

The Nottingham defendants were charged with conspiracy to commit aggravated trespass, and argued that they acted through "necessity" to prevent death and serious injury caused by CO2 emissions and climate change.

Their own powerful testimony was supported by leading professors on epidemiology and population health who confirmed that climate change is currently contributing towards an additional 150,000 deaths each year around the world. It will only get worse.

The Greenpeace defendants were tried for criminal damage to the power station's chimney and argued that they had "lawful excuse" for their actions: they sought to protect property around the world threatened by climate change. Again, their vivid accounts of melting ice caps, expanding oceans and deforestation – and resulting erratic weather, flooding and rising sea levels - were supported by expert evidence.

However, in both cases the jury had to consider one simple proposition: did the defendants believe their action was imperative, urgent and reasonable – in the light, among other things, of politicians' inactivity and nature's "tipping points" (the points of no return when runaway climate change will be beyond our control).

Given the inviolability of the jury's deliberations, we can only speculate on their decision making. The Nottingham jury may have been influenced by the crown's argument that instead of taking "direct action", the defendants should have spent their money paying a celebrity to front a campaign – or should have installed a biodegradable toilet in their homes, as the prosecutor confided she had. They might have derived some advantage – not immediately obvious to others in court – from the calculator they asked to take with them to assist their deliberations on the defendants' guilt or innocence.

More seriously, one might speculate what has happened in the two years since the Maidstone verdict in 2008? In the science world, "climategate" has been exploited by "contrarians" to reduce the proportion of the population who are concerned about climate change, even as mean world temperatures rise. Internationally, the Copenhagen and Cancún summits have failed to provide legally binding and effective agreements to tackle climate change. In the UK, the focus is on the reduction of the deficit through pinching financial short-termism. In an austere new world, the public may be less receptive to arguments of morality and altruism which recognise our responsibility to the world community and future generations.

The two juries' verdicts of course have no binding effect in future cases, but one ruling from the Nottingham case does. The crown tried, at a pre-trial hearing, to prevent the Nottingham jury even hearing the defendants' case.

On 21 May 2010 a high court judge rejected that argument, saying that "the circumstances in which a court will withdraw a defence from the jury will be very rare indeed". This may be the legacy of the Nottingham defendants.